The Tigers snapped up the former Wigan and Saints back-row after he was deemed surplus to requirements at the Galpharm Stadium.
A delighted Cas boss Terry Matterson said: "I am very pleased to welcome Stuart on board. He has plenty of Super League experience but still relatively young with his best years ahead of him. He has initially agreed a one-year deal but I am expecting him to be determined to win a longer one.
"Stuart is a strong defender and runner with an outstanding work ethic and I feel that he will prove a very valuable addition to our pack, which is beginning to look a strong unit as we build for 2009.
"Stuart is the first of the English-based players who we are hoping to be able to bring on board but we are progressing on other fronts and we expect to be in a position to make further announcements in the coming weeks."
Jones, 26, started his Super League career with his hometown of Wigan in 2002 before a two-season stint at Knowsley Road. He joined the Giants in 2004, when he also won an England call-up, and has been a regular in the Huddersfield line-up since then, as well as appearing in the club's Challenge Cup Final appearance in 2006.
He said: "I am very excited about the move. I have had five years with Huddersfield and it is time for a new challenge and a new experience. Castleford are a club with a lot of ambition, they have the licence and they are looking to move on to the next stage and get into the top-six and I am looking forward to helping them to achieve that."
Jones is the club's fourth new recruit for 2009 following the recent captures of Rangi Chase, Dean Widders and Sione Faumuina. Giants' hooker Ryan Hudson and Bradford three-quarter James Evans are expected to be confirmed as Cas players in the next few days.
Meanwhile, head coach Matterson wants the Tigers to make Saturday's final-day clash with Bradford a memorable occasion.
The Bulls need a win to have a chance of pipping Warrington and Wigan for fourth place but Matterson insists Cas can spoil the party.
"It's massively important to sign off on a win," said the Cas boss. "You always remember the last game. Two years ago it took us a long time to forget it but last year it was fantastic and hopefully the boys can draw on some of that.
"It's a funny one to have a week off before the last game but the players have come back pretty good and determined to finish the season on the right note.
"With Awen (Guttenbeil) retiring and the futures of quite a few others still up in the air, this is the last time this group of people will play together. They got a lot of enjoyment out of our last performance against Warrington.
"Bradford are a good side with a lot to play for and this is perfect preparation for the semis. But there is a lot of pride in our team and it's all set up for a cracking game."
Guttenbeil is expected to feature, despite a hamstring strain, but Joe Westerman and Brent Sherwin, who both missed the last game, are doubtful. Said Matterson: "I can't see there being too many changes. I'd like to give Adam Fletcher a run but the main thing is to get our best team out there."
Matterson admits the RFL's decision to relax the rules on homegrown players may have come too late to force a re-think over his re-building plans for 2009.
It means clubs are now able to renew or extend the contracts of non-Federation players over and above the current limit (eight), providing those players were under contract prior to the introduction of the RFL's club-trained player rules in June 2007.
It opens the door for Cas to re-sign Andy Henderson, Mark Leafa and Adam Fletcher but Matterson said: "You plan your budgets that some people aren't going to be available and three days before the deadline they hit you with that one. It's made us go back and see if we can do anything different but we're so far down the track at the moment it's difficult."
Castleford have awarded teenage prop Jon Walker a two-year Academy contract for 2009 and 2010. The Bradford-born 17-year-old was named the Academy's most improved player at last week's awards dinner.